Wafer handling method for use in lithography patterning

ABSTRACT

A method utilizing a lithography system comprises a lithography patterning chamber, a wafer exchange chamber separated from the lithography patterning chamber by a first gate valve, and at least one alignment load-lock separated from the wafer exchange chamber by a second gate valve. The alignment load-lock includes an alignment stage that aligns a wafer during pump-down. The alignment load-lock can be uni-directional or bi-directional. The lithography system can include one or multiple alignment load-locks.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/896,057, filed Jul. 22, 2004 (now U.S. Pat. 6,927,842 that issuedAug. 9, 2005), which is a continuation of U.S. application Ser. No.09/981,992 filed Oct. 19, 2001 (now U.S. Pat. No. 6,778,258 that issuedAug. 17, 2004), which are incorporated by reference herein in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer handling system and method foruse within a lithography system. More particularly, this inventionrelates to a system and method of wafer handling in which wafers aretransported within a lithography system while being affixed and alignedto chucks, thereby maximizing production throughput.

2. Related Art

Lithography is a process used to create features on the surface ofsubstrates. Such substrates can include those used in the manufacture offlat panel displays, circuit boards, various integrated circuits, andthe like. A frequently used substrate for such applications is asemiconductor wafer. While this description is written in terms of asemiconductor wafer for illustrative purposes, one skilled in the artwould recognize that this description also applies to other types ofsubstrates known to those skilled in the art. During lithography, awafer, which is disposed on a wafer stage, is exposed to an imageprojected onto the surface of the wafer by exposure optics locatedwithin a lithography apparatus. While exposure optics are used in thecase of photolithography, a different type of exposure apparatus may beused depending on the particular application. For example, x-ray, ion,electron, or photon lithographies each may require a different exposureapparatus, as is known to those skilled in the art. The particularexample of photolithography is discussed here for illustrative purposesonly.

The projected image produces changes in the characteristics of a layer,for example photoresist, deposited on the surface of the wafer. Thesechanges correspond to the features projected onto the wafer duringexposure. Subsequent to exposure, the layer can be etched to produce apatterned layer. The pattern corresponds to those features projectedonto the wafer during exposure. This patterned layer is then used toremove exposed portions of underlying structural layers within thewafer, such as conductive, semiconductive, or insulative layers. Thisprocess is then repeated, together with other steps, until the desiredfeatures have been formed on the surface of the wafer.

Step-and-scan technology works in conjunction with a projection opticssystem that has a narrow imaging slot. Rather than expose the entirewafer at one time, individual fields are scanned onto the wafer one at atime. This is done by moving the wafer and reticle simultaneously suchthat the imaging slot is moved across the field during the scan. Thewafer stage must then be stepped between field exposures to allowmultiple copies of the reticle pattern to be exposed over the wafersurface. In this manner, the sharpness of the image projected onto thewafer is maximized. Through increases in both alignment precision andprojection accuracy, today's lithography tools are capable of producingdevices with ever decreasing minimum feature size. However, minimumfeature size is but one measure of a lithography tool's utility. Anothercritical measure is throughput.

Throughput refers to the number of wafers per hour that can be patternedby a lithography system. Every task that must be performed on waferswithin a lithography system contributes to the total time required topattern the wafers, with an associated decrease in throughput. Onecritical task that must be performed repeatedly within a lithographysystem is wafer alignment. Wafers must be precisely aligned within alithography system in order to achieve high levels of overlay accuracy.Unfortunately, alignment precision is usually lost whenever wafers aremoved within conventional lithography systems with robots.

What is needed is a system and method for handling wafers within alithography system that both avoids the loss of alignment caused byconventional robots, while at the same time improving system throughput.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a lithography systemhaving a lithography patterning chamber, a wafer exchange chamberseparated from the lithography patterning chamber by a first gate valve,and at least one alignment load-lock separated from the wafer exchangechamber by a second gate valve. The alignment load-lock includes analignment stage that aligns a wafer during pump-down. An alignmentload-lock according to the present invention can be uni-directional orbi-directional. Likewise, a lithography system according to the presentinvention can include one or multiple alignment load-locks.

A lithography system according to the present invention can also includea holding load-lock separated from the wafer exchange chamber.

A lithography system according to the present invention can furtherinclude an illumination source that emits light having an inspectionwavelength, and a camera sensitive to said inspection wavelength. A roofof the alignment load-lock is transparent to the inspection wavelengthto allow observation of the wafer contained within the alignmentload-lock.

Also included within the alignment load lock according to an embodimentof the present invention are supports for holding a wafer. Thesesupports can be hooks, pins, and the like. An alignment stage is furtherlocated within the alignment load lock. The alignment stage is separatedfrom an alignment sub-stage disposed outside of the alignment load-lockby a column extending through a floor of the alignment load-lock.Furthermore, the floor of the alignment load-lock can include a motionfeedthrough seal that allows the column to move relative to the floorwhile preventing gas flow into the alignment load-lock. Such a motionfeedthrough seal can include bellows and rotary seals such asferromagnetic seals.

Further included in an embodiment of the present invention are multiplechucks. The chucks can be electrostatic chucks or vacuum chucks. Thechucks can include cutouts for accommodating the wafer supports withinthe alignment load-lock. The chucks can further include chuck engagementmechanisms for kinematically mounting the chucks to the alignment stageor to a stage located within the lithography patterning chamber. Incritical areas, the chuck engagement mechanisms can be kinematichemispheres in order to avoid stress and strain, including, for example,hemispheres for engagement with vee-blocks located on the various stageswithin the lithography system.

In an embodiment of the present invention, the lithography patterningchamber can include multiple exposure stages.

Also disclosed is a method of patterning a wafer within a lithographysystem. In an embodiment, the method includes a first step of placingthe wafer on supports within an alignment load-lock. In a next step, thewafer is aligned with respect to a chuck while the wafer is supportedwithin the alignment load-lock on the supports. In another step, thewafer is secured to the chuck. And in yet another step, pump-down isperformed to create a vacuum within the alignment load-lock.

In a method according to the present invention, pump-down can beperformed concurrently with aligning the wafer relative to the chuck.Likewise, pump-down can be performed concurrently with securing thewafer to the chuck subsequent to the alignment step.

A method according to an embodiment of the present invention can alsoinclude a step of transporting the chuck and wafer to a lithographypatterning chamber. Further fine alignment may be needed in thelithography patterning chamber. Next, a step of performing lithographypatterning on the wafer is conducted. Once the lithography patterning iscomplete, the wafer and chuck are returned to the alignment load-lockarea. Once back at the alignment load-lock, the chuck can be removedfrom the wafer and venting can be performed. The venting can take placewhile the wafer is being removed from the chuck.

Also disclosed herein is a method of aligning a wafer within analignment load-lock. In an embodiment, this method includes a first stepof placing the wafer on supports within the alignment load-lock. Next, astep of observing the location and orientation of the wafer on thesupports within the alignment load-lock is performed. Also performed isa step of moving a chuck so as to align the wafer with respect to thechuck. Once aligned, the chuck is then placed in contact with, andsecured to, the wafer. The step of observing the location andorientation of the wafer can be performed by a camera located outside ofthe alignment load-lock.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, are illustrations of the present invention and,together with the description, further serve to explain the principlesof the invention and to enable a person skilled in the pertinent art tomake and use the invention. Like reference numbers refer to likeelements within the different FIGs.

FIG. 1 is an illustration of a lithography system according to thepresent invention.

FIG. 2A is an exploded view of the upper elements within an alignmentload-lock according to the present invention.

FIG. 2B is an exploded view of the lower elements within an alignmentload-lock according to the present invention.

FIG. 3A is an illustration of a floor-mounted motion feedthrough 300within a lithography system according to the present invention.

FIG. 3B is an illustration of a wall-mounted motion feedthrough 350within a lithography system according to the present invention.

FIG. 4A is an illustration of a method of patterning a wafer within alithography system utilizing a bidirectional load-lock(s) according tothe present invention.

FIG. 4B is an illustration of a method of patterning a wafer within alithography system utilizing a unidirectional load-lock(s) according tothe present invention.

FIG. 5 is an illustration of a method of aligning a wafer within analignment load-lock according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term wafer means a semiconductor wafer, or any othersubstrate suitable for lithographic patterning.

Alignment, pump-down, and charging of an electrostatic chuck are allprocedures that take up precious time within a lithography patterningprocess. The present inventors have discovered that all three of thesefunctions can be combined into a single alignment load-lock station.Such a single alignment load-lock station can align a wafer with respectto a chuck and then secure that wafer to the chuck, all the whilepumping-down the load-lock. By including more than one chuck within sucha lithography system, wafers can be secured to their respective chucksduring lithography patterning, thereby maximizing throughput.

FIG. 1 is an illustration of a lithography system 100 according to thepresent invention. Lithography system 100 patterns wafers, indicated bydashed circles within the FIG., that are obtained from a track 101.Wafers obtained from track 101 have undergone various processes asrequired prior to lithography patterning. For example, resist-apply,pre-bake, and other processes known to those skilled in the relevantart(s) are conducted on wafers prior to lithography patterning. Afterlithography patterning, wafers are returned to the track for furtherprocessing steps, such as development, post bake, and the like. Track101 is connected to lithography system 100 via two gate valves 102, 103.Gate valves 102, 103 are of the type known to those skilled in therelevant art(s) as being capable of maintaining different atmosphericpressures on either side of the gate valve. Gate valves 102, 103separate track 101 from two alignment load-locks 104, 105.

Alignment load-locks 104, 105 are separated from a wafer exchangechamber 106 by gate valves 107, 108. Gate valves 107, 108 are analogousto gate valves 102, 103 that connect alignment load-locks 104, 105 tothe track 101. Each alignment load-lock 104, 105 is thus a chamberseparated from track 101 and wafer exchange chamber 106 by respectivegate valves. Alignment load-locks 104, 105 are further connected tovacuum and venting elements (not shown) that allow the alignmentload-locks to be transitioned from atmospheric pressure to vacuum(pumped-down) and back to atmospheric pressure again (vented). In thisway, wafer exchange chamber 106 can be held at a high vacuum while track101 is held at atmospheric pressure. Alignment load-locks 104, 105 thusserve to move wafers in and out of the wafer exchange chamber whiletransitioning from atmospheric pressure to high vacuum. The presentinventors have discovered that by including alignment and chuckingfeatures within alignment load-locks 104, 105, overall system throughputcan be greatly enhanced. Alignment load-locks 104, 105 will be discussedin greater detail below in connection with FIGS. 2 a and 2 b.

Wafer exchange chamber 106 includes a robot 109 having a dualend-effector. Robot 109 is vacuum compatible and is capable of handlingtwo chucks at once by virtue of its dual end-effector. Alternatively,other structures can be used to transport the chuck with aligned waferfrom the alignment load-lock to the lithography patterning chamber aswould apparent to those skilled in the relevant arts given thisdisclosure. For example, a robot having a single end-effector, or dual,non-robotic, transport mechanisms could also be used without departingfrom the scope of the present invention.

Wafer exchange chamber 106 is connected to lithography patterningchamber 111 by gate valve 110. Gate valve 110 is similar to the othergate valves described herein. Lithography patterning chamber 111includes wafer stages 112, 113. Wafer stages 112, 113 are capable ofmovement in the directions indicated for fine alignment and exposureprocesses. Lithography patterning chamber 111 thus further includesprojection optics or other elements necessary to perform the lithographypatterning. While lithography patterning chamber 111 includes two waferstages 112, 113 a lithography patterning chamber could also include onewafer stage. A dual wafer stage structure like that shown is describedin more detail in co-pending, commonly owned U.S. patent applicationSer. No. 09/449,630, titled “Dual-Stage Lithography Apparatus andMethod,” filed Nov. 30, 1999, which is hereby incorporated by referencein its entirety.

Lithography system 100 further includes a holding load-lock 114. Holdingload-lock 114 is used to hold a spare chuck, or to exchange chuckswithin the lithography system while maintaining lithography patterning.This allows access to a chuck held in holding load-lock for cleaning,for example. Holding load-lock 114 also includes gate valves 115 and116. While the presence of holding load-lock is preferable, as it allowschuck exchange without stopping lithography patterning, it can beomitted without departing from the scope of the present invention.

While alignment load-locks 104, 105, and holding load-lock 114 are allpreferably bi-directional load-locks, uni-directional load-locks couldalso be used without departing from the scope of the present invention.Unidirectional load-locks are capable of wafer input or wafer outputonly. Bidirectional load-locks, however, are capable of both wafer inputand wafer output.

For example, if the wafer is transferred from track 101 to aunidirectional alignment load-lock and then to patterning chamber 111,it cannot then be transferred to the same unidirectional alignmentload-lock after it has been patterned. Rather, after the patterningprocess is completed in the lithography patterning chamber, the wafermust instead be returned to another alignment load-lock and then, inturn, to track 101.

By contrast, if the wafer is transferred from track 101 to abidirectional alignment load-lock and then to lithography patterningchamber 111, after patterning, the wafer can be transferred back throughthe same bidirectional alignment load-lock to track 101.

While the use of two bi-directional alignment load-locks is advantageousas it allows for greater system throughput, two single unidirectionalload-locks could also be used. Likewise, a single bi-directionalalignment load-lock could also be used without departing from the scopeof the present invention. The precise structure and function of each ofalignment load-locks 104, 105 will now be described in connection withFIGS. 2A and 2B.

FIGS. 2A and 2B together constitute an exploded view of the elementswithin an alignment load-lock according to the present invention. FIG.2A corresponds to the upper portion of an alignment load-lock accordingto the present invention, while FIG. 2B corresponds to the lower portionof an alignment load-lock according to the present invention. The wallsof the alignment load-lock are not shown in either of FIG. 2A or 2B.

Alignment load-lock roof 201 is an airtight transparent orsemi-transparent window. A camera 202 and an illumination source 203 aredisposed above alignment load-lock roof 201. By “semi-transparent,” itis meant that alignment load-lock roof 201 is at least transparent to aninspection wavelength of light emitted from illumination source 203 towhich camera 202 is sensitive. Within the alignment load-lock are wafersupports 204, 205, 206. These wafer supports 204–206 are used to hold awafer 207. Wafer supports 204–206 are illustrated in the FIG. as hooks,but could also comprise pins, or other supporting mechanisms, as wouldbe apparent to one skilled in the relevant art(s). Wafer 207 has beenplaced on wafer supports 204–206 from track 101 by an additional robot,which is customarily part of the track system (not shown). Moreover,wafer 207 can undergo prior coarse alignment so that notch 208 or otherdesired feature is placed within a field of view 209 of the camera 202,which is within an illumination field 210 of the illumination source203. Such prior coarse alignment can be accomplished in a manner knownto those skilled in the relevant art(s). For example, it can beperformed by a module in the track that spins the wafer and locates thenotch using a photoelectric sensor. Also included within the alignmentload-lock shown is a chuck 211 having chuck cutouts 212, 213, and 214.Chuck cutouts 212–214 are large enough to accommodate a range of motionif the chuck such that wafer supports 204–206 can be accommodated withinthese chuck cutouts 212–214. Thus, chuck cutouts 212–214 line upapproximately with wafer supports 204–206.

FIG. 2B corresponds to the bottom portion of the alignment load-lock.Specifically, alignment load-lock floor 216 having a motion feedthroughseal 217 is located at a bottom portion of the alignment load-lock.Motion feedthrough seal 217 allows movement of a column 230, upon whichis disposed an alignment stage 218, with respect to the load-lock floorwhile preventing gas from flowing into the load lock. In the particularembodiment shown, motion feedthrough seal 217 comprises bellows thatwill be described below in greater detail with respect to FIG. 3.Alternatively, other types of motion feedthrough seals, such as amovable seal or a ferrofluidic seal, could be used without departingfrom the scope of the present invention.

Alignment stage 218 include stage engagement mechanisms 219, 220, and221. Stage engagement mechanisms are used for kinematically mounting thechuck 211 with chuck engagement mechanisms 222–224 disposed on the lowersurface of the chuck 211. In critical areas, the chuck engagementmechanisms can be kinematic hemispheres in order to avoid stress andstrain, including, for example, hemispheres for engagement withvee-blocks 219–221 located on the various stages within the lithographysystem. In the embodiment shown, stage engagement mechanisms 219–221comprise vee-blocks 219–221 that constitute the bottom half of akinematic mount. Likewise, in the embodiment shown, chuck engagementmechanisms 222–224 comprise hemispheres that constitute the top half ofthe kinematic mount. As would be apparent to one skilled in the relevantart(s) given this description, other types of kinematic mounts can beused without departing from the scope of the present invention.

In the embodiment shown, chuck 211 is an electrostatic chuck capable ofmaintaining an electric charge sufficient to hold a wafer for anextended period of time. In one embodiment, however, chuck 211 is avacuum chuck. Alignment stage 218 further includes contact block 225,having pogo contacts 226 and 227. Pogo contacts 226, 227 are used tomake electrical contact with contact pads 228 and 229 disposed on thebottom of chuck 211. In one embodiment, pogo contacts 226 and 227 arespring-loaded contacts made of metal tubing. The metal tubing comprisesa spring with a metal bar. The metal bar contacts the contact pads 228and 229. Chuck 211 is charged and discharged through contact pads 228and 229 when connected to pogo contacts 226 and 227. While the presentinvention is described in terms of an electrostatic chuck, other chuckscan be used without departing from the scope of the present invention.For example, vacuum chucks, mechanical clamping, and other means ofsecuring a wafer to a chuck could be used, as would be apparent to oneskilled in the relevant art(s). Due to the high vacuum environment inwhich extreme ultraviolet light processing occurs, electrostatic chucksare preferable.

Alignment stage 218 is positioned at the top of column 230. Column 230is disposed atop an alignment substage 231, which is held by analignment substage mount 232. Additional motor and control elements (notshown) are used to move the alignment stage in four degrees of freedom(rotation, two horizontal translations, and a vertical translation) andas indicated by the arrows in the FIG., as would be apparent to a personskilled in the relevant art(s), given this description. Motionfeedthrough seal 217 serves to separate the high vacuum environmentwithin the alignment load-lock from the alignment substage 231,alignment substage mount 232, and the remainder of the lithographysystem.

Operation of the elements within the alignment load-lock will now bedescribed. It should be noted that chuck 211 and wafer 207 are notintegral parts of the alignment load-lock. Rather, chuck 211 is one of anumber of like chucks which are used within the lithography system 100.Likewise, wafer 207 has been obtained from track 101 for lithographypatterning within lithography patterning chamber 111, of the systemshown in FIG. 1. As mentioned above, wafer 207 may have undergone coarsealignment prior to being placed on wafer supports 204–206. This coarsealignment can be performed in order to place notch 208 within the fieldof view 209 of camera 202. Since camera 202 can see notch 208, thecamera 202 can determine both the center of the wafer from the radius ofcurvature visible within the field of view 209 as well as theorientation of the wafer from the location of notch 208. In thisrespect, it should be noted that while one camera 202 has been shown inFIG. 2A, a plurality of such cameras and light sources 203 can be usedwithout departing from the scope of the present invention. Since camera202 is used for determining notch location 208 as well as the radius ofcurvature of wafer 206, the use of more than one camera can increase theprecision of the observations, as would be apparent to one skilled inthe relevant art(s) given this disclosure. Best results would beobtained with two diametrically opposed cameras (or equally spacedcameras, in reference to the wafer).

Camera 202 looks at field of view 209 to determine wafer location 207.This wafer location is then output by camera 202 to a patternrecognition unit 233 (not shown). The pattern recognition unit sendslocation information to alignment substage 232. Since the patternrecognition unit knows the precise orientation and location of wafer 207it can control the location of alignment stage 218 through alignmentsubstage 231 and alignment substage mount 232. Once chuck 211 has beenaligned with wafer 207, chuck 211 is moved up to and put in contact withwafer 207. Once in contact with wafer 207, chuck 211 is charged throughcontact pads 228 and 229, which are in contact with pogo contacts 226and 227 at contact block 225 of alignment stage 218. Since chuck 211 hasbeen aligned with wafer 207 prior to chuck 211 being charged, wafer 207is firmly held in contact with chuck 211 by virtue of the charge. Sinceeach wafer stage 112, 113 within lithography patterning chamber 111includes kinematic mounts, the repeatability of chuck placement on waferstages 112, 113 within the lithography patterning chamber is limited tothe accuracy of the kinematic mounts. The kinematic mounts shown, whichuse vee-blocks and hemispheres, have a repeatability of about twomicrons. Since chuck 211 can maintain its electrostatic charge withinthe lithography system 100, the alignment of a wafer, for example, wafer207, will always be within the repeatability of the kinematic mountsused.

Returning to FIG. 1, it should be apparent from the above discussion inconnection with FIGS. 2A and 2B that while a wafer is within either ofalignment load-locks 104 or 105, alignment and chucking operations canbe performed while the alignment load-lock is undergoing pump-down. Oncea wafer within alignment load-lock 104 or alignment load-lock 105 hasbeen aligned with respect to a chuck and attached to that chuck, andpumpdown is complete, the gate valve 107, or 108, can be opened, atwhich point robot 109 can lift the chuck and wafer together from withineither alignment load-lock and move it to the lithography patterningchamber 111. Since robot 109 includes a gripper, it can hold two chucksat once. Thus, robot 109 can swiftly exchange chucks between eitheralignment load-lock station and either wafer stage.

FIG. 3A is an illustration of a floor-mounted motion feedthrough 300within a lithography system of the present invention. Bellows 302 allowvertical and horizontal translations of shaft 230 relative to load-lockfloor 216, while maintaining vacuum inside the load lock. Bellows 302include a plurality of metal, preferably stainless steel disks welded attheir peripheral and inside edges. These bellows allow column 230 tomove in six degrees of freedom while maintaining a vacuum seal. Rotaryseal 304 allows rotation of shaft 230, while maintaining a vacuum.Bearing 306 captures shaft flange 308, preventing collapse of thebellows due to atmospheric pressure. It will be apparent to one skilledin the art that seal 304 can be an elastomer seal, a pre-loaded teflonseal, or a ferrofluidic seal. It will also be apparent that the transferof rotary motion accomplished by 304–308 could have also beenaccomplished via a magnetic coupling.

FIG. 3B is an illustration of a wall-mounted motion feedthrough 350within a lithography system of the present invention. Bellows 352,attached to chamber wall 354, allows vertical and horizontal translationof alignment stage 218. Bellows 352 also allow a limited amount ofrotation of alignment stage 218 about its centerline 356. Thisarrangement does not require a rotary seal, and is, therefore, lessleak-prone than the apparatus of FIG. 3A. However, whereas the rotaryseal 304 of FIG. 3A allows unlimited rotation, the bellows 352 onlyallow a few degrees of rotational freedom. The limited amount ofrotation is sufficient if a coarse alignment step is performed on thewafer (by the track) before introducing the wafer in the load-lock. Itwill be understood that a second wall-mounted feedthrough mechanismcould be added diametrically opposite to the one shown through a hole inan opposite wall in order to improve mechanical stability of theapparatus, without deviating from the present invention.

FIG. 4A is an illustration of a method 400 of patterning a wafer withina lithography system utilizing at least one bidirectional alignmentload-lock according to the present invention. It should be noted thatsuch a system can comprise only one bidirectional alignment load-lock ora plurality of bidirectional alignment load-locks to increase efficiencyand throughput. In the embodiment utilizing a bidirectional alignmentload-lock system, unlike the embodiment utilizing a unidirectionalalignment load-lock system, the bidirectional alignment load-lock(s) iscapable of accepting the wafer from track 101 as it enters thelithography system (input) and also allowing the wafer to enter it afterpatterning and be dispelled from it back to track 101 (output). In otherwords, the wafer can be transferred from track 101 to the bidirectionalalignment load-lock, from the bidirectional alignment load-lock to thepatterning chamber, from the patterning chamber after patterning to thesame bidirectional alignment load-lock, and then from the bidirectionalalignment load-lock to the track 101.

In a first step 410 of the method 400 of FIG. 4A, a wafer is placed onwafer supports within a bidirectional alignment load-lock(s). Asdescribed above in connection with FIG. 1, the wafer can be taken from atrack before being placed onto supports within the bidirectionalalignment load-lock(s). Placing the wafer on the supports within thebidirectional alignment load-lock(s) can be accomplished with, forexample, a robot. As described above in connection with FIG. 2A, thewafer supports within the bidirectional alignment load-lock(s) cancomprise hooks, pins, and the like. Also, as described above inconnection with FIG. 1, the bidirectional alignment load-lock(s) cancomprise a conventional load-lock chamber with gate valves separating atrack from a wafer transport chamber. In a lithography system operatingat high vacuum, such a wafer transport chamber would be kept at highvacuum while the track would be kept at atmospheric pressure. Thebidirectional alignment load-lock(s) is thus used to transfer wafers inand out of the high vacuum environment within the lithography apparatusitself without exposing the entire apparatus to atmospheric pressure.

In a next step 420, the wafer is aligned with respect to a chuck. Asdescribed elsewhere herein, the chuck can be an electrostatic chuck, avacuum chuck, or a chuck with other mechanical clamping features. In anext step 421, the aligned wafer is secured to the chuck. The securingof the aligned wafer to the chuck 421 can be accomplished by moving thechuck up to and in contact with the wafer and then, in the case of anelectrostatic chuck, charging the electrostatic chuck to thereby securethe wafer to the chuck. Such charging can be accomplished through theuse of pogo contacts on an alignment stage which are in contact withpads on the bottom surface of the electrostatic chuck. Further detailsof steps 420 and 421 are described in greater detail below in connectionwith FIG. 5.

In a step 425, concurrent with at least one or both of steps 420 and421, a pump-down is performed within the bidirectional alignmentload-lock(s). As is known to those skilled in the relevant art(s),pump-down is the procedure whereby the load-lock is evacuated of gasesthus bringing it from atmospheric pressure to high vacuum. As describedelsewhere herein, the present inventors have discovered that byperforming the pump-down operation simultaneously with the alignment ofthe wafer with respect to the chuck and the securing of the wafer to thechuck, greater throughput can be realized within a lithography systemaccording to the present invention.

In a next step 430, the chuck with the aligned wafer is transported to alithography patterning chamber. As described above in connection withFIG. 1, the transportation of the chuck from the bidirectional alignmentload-lock(s) to the lithography patterning chamber can be accomplishedby a robot located within a wafer exchange chamber disposed between thebidirectional alignment load-lock(s) and the lithography patterningchamber. Such a robot can have a dual end defector to realize greaterefficiency of transportation of chucks between bidirectional alignmentload-lock(s) and the lithography patterning chamber. Alternatively,other structures can be used to transport the chuck with aligned waferfrom the bidirectional alignment load-lock(s) to the lithographypatterning chamber, as would apparent to those skilled in the relevantart(s) given this disclosure. For instance, the chuck and wafer could beplaced on a kinematic mount of the exposure stage.

Once the chuck with aligned wafer have been placed into the lithographypatterning chamber, lithography patterning is performed in a next step440. Such lithography patterning can include a final alignment step aswell as additional steps used within lithography patterning as are knownto those skilled in the relevant art(s).

In a next step 450, the chuck with processed wafer are removed from thekinematic mount of the exposure stage to a bidirectional alignmentload-lock(s) from the lithography patterning chamber. As described abovein connection with step 430, the transportation of the chuck with theprocessed wafer from the lithography patterning chamber to thebidirectional alignment load-lock(s) can be performed with a robotlocated within a wafer exchange chamber. Moreover, the chuck withpatterned wafer can be brought back to the same bidirectional alignmentload-lock(s) through which it entered the system.

In a next step 460, the processed wafer is removed from the chuck withinthe bidirectional alignment load-lock(s). This step is substantially thereverse of process step 421, discussed above. Thus, once the chuck withpatterned wafer is returned to the bidirectional alignment load-lock(s),the chuck can be discharged. Once discharged, the chuck can be loweredaway from the wafer leaving the wafer held by the wafer supports.Concurrently with step 460, a venting operation is performed at aconcurrent step 465. Venting is the process by which the pressure withinthe bidirectional alignment load-lock(s) is brought from high vacuumback to atmospheric pressure. As with steps 420, 421, and 425, theventing step 465 is performed simultaneously with step 460. As with thepump-down process, performing venting while removing the wafer from thechuck further increases the throughput of a lithography system accordingto the present invention.

In a final step 470, the now patterned wafer is removed from thebidirectional alignment load-lock(s) and placed back onto the track.Alternatively, the wafer can be placed onto another structure used tomove wafers away from the lithography apparatus. As will be apparent toa person skilled in the relevant arts, after the final step 470 of themethod 400 of FIG. 4 has been performed, the lithography system has beenreturned to its condition existing prior to the first step, 410.Accordingly, method 400 can be repeated indefinitely for the lithographypatterning of multiple wafers.

FIG. 4B is an illustration of a method 472 of patterning a wafer withina lithography system utilizing unidirectional alignment load-lock(s)according to the present invention. In a first step 474 of the method472 of FIG. 4B, a wafer is placed on wafer supports within an inputalignment load-lock. The input alignment load-lock is unidirectional, asthe wafer does not exit the system through the same alignment load-lockthrough which it entered the system. Rather, it is returned to anotheralignment load-lock (output alignment load-lock) after it undergoespatterning in the patterning chamber and exits the system (i.e.,transferred to track 101) through the output alignment load-lock. Asdescribed above in connection with FIG. 1, the wafer can be taken from atrack before being placed onto supports within the input alignmentload-lock. Placing the wafer on the supports within the input alignmentload-lock can be accomplished with, for example, a robot.

As described above in connection with FIG. 2A, the wafer supports withinthe input alignment load-lock can comprise hooks, pins, and the like.Also, as described above in connection with FIG. 1, the input alignmentload-lock can comprise a conventional input load-lock chamber with gatevalves separating a track from a wafer transport chamber. In alithography system operating at high vacuum, such a wafer transportchamber would be kept at high vacuum while the track would be kept atatmospheric pressure. The input alignment load-lock is thus used totransfer wafers into the high vacuum environment within the lithographyapparatus itself without exposing the entire apparatus to atmosphericpressure.

In a next step 476, the wafer is aligned with respect to a chuck. Asdescribed elsewhere herein, the chuck can be an electrostatic chuck, avacuum chuck, or a chuck with other mechanical clamping features. In anext step 478, the aligned wafer is secured to the chuck. The securingof the aligned wafer to the chuck can be accomplished by moving thechuck up to and in contact with the wafer and then, in the case of anelectrostatic chuck, charging the electrostatic chuck to thereby securethe wafer to the chuck. Such charging can be accomplished through theuse of pogo contacts on an alignment stage which are in contact withpads on the bottom surface of the electrostatic chuck. Further detailsof steps 476 and 478 are described in greater detail below in connectionwith FIG. 5.

In a step 480 concurrent with at least one or both of steps 476 and 478,a pump-down is performed within the input alignment load-lock.

In a next step 482, the chuck with the aligned wafer is transported to alithography patterning chamber. As described above in connection withFIG. 1, the transportation of the chuck from the input alignmentload-lock to the lithography patterning chamber can be accomplished by arobot located within a wafer exchange chamber disposed between the inputalignment load-lock and the lithography patterning chamber.Alternatively, other structures can be used to transport the chuck withaligned wafer from the input alignment load-lock to the lithographypatterning chamber, as would apparent to those skilled in the relevantart(s) given this disclosure. For instance, the chuck and wafer could beplaced on a kinematic mount of the exposure stage.

Once the chuck with aligned wafer have been placed into the lithographypatterning chamber, lithography patterning is performed in a next step484. Such lithography patterning can include a final alignment step aswell as additional steps used within lithography patterning as are knownto those skilled in the relevant art(s).

In a next step 486, the chuck with processed wafer are removed from thekinematic mount of the exposure stage to an output alignment load-lockfrom the lithography patterning chamber. It should be noted that theoutput alignment load-lock is not the same alignment load-lock as theinput alignment load-lock. The wafer is only transferred through theoutput alignment load-lock after it has exited the lithographypatterning chamber and needs to be transferred back to track 101. Asdescribed above in connection with step 482, the transportation of thechuck with the processed wafer from the lithography patterning chamberto the output alignment load-lock can be performed with a robot locatedwithin a wafer exchange chamber.

In a next step 488, the processed wafer is removed from the chuck withinthe output alignment load-lock. This step is substantially the reverseof process step 478, discussed above. Thus, once the chuck withprocessed wafer is transferred to the output alignment load-lock, thechuck can be discharged. Once discharged, the chuck can be lowered awayfrom the wafer leaving the wafer held by the wafer supports.Concurrently with step 488, a venting operation is performed at aconcurrent step 490. As with steps 476, 478, and 480, the venting step480 is performed simultaneously with step 476.

In a final step 492, the now processed wafer is removed from the outputalignment load-lock and placed back onto the track. Alternatively, thewafer can be placed onto another structure used to move wafers away fromthe lithography apparatus. As would be apparent to a person skilled inthe relevant arts, after the final step 492 of the method 472 of FIG. 4Bhas been performed, the lithography system has been returned to itscondition existing prior to the first step, 474. Accordingly, method 472can be repeated indefinitely for the lithography patterning of multiplewafers.

FIG. 5 is an illustration of a method 500 of aligning a wafer within analignment load-lock according to the present invention. In a first step510, a wafer is placed on wafer supports. As discussed elsewhere herein,such wafer supports can include hooks, pins, and the like. Also asdiscussed elsewhere herein, the wafer can be placed on the wafersupports through the use of a robot or other wafer transport mechanisms,as would be apparent to one skilled in the relevant art(s).

In a next step 520, the wafer's orientation and location is observed.Such observation can be conducted, for example, with a camera andillumination source located outside of the alignment load-lock, asdescribed above in connection with FIG. 2A. The wafer's location isobserved by the camera by analyzing the wafer's radius of curvatureobserved within the camera's field of view. The term location as usedherein in connection with a wafer means the location of the wafer withinan XY plane. Thus, by viewing the radius of curvature of the wafer, thelocation of the center of the wafer can be determined with a patternrecognition unit. Such pattern recognition units and their operation inconnection with a camera and illumination source like the type describedherein are well known to those skilled in the relevant art(s).

The wafer's particular orientation (i.e. its angular orientation aboutits center) is determined by noting the location of a notch within thewafer that is also located within the camera's field of view. In orderto assure that the notch is located within the camera's field of viewupon initial observation, coarse alignment can take place prior to themethod shown in FIG. 5. Such coarse alignment can include, for example,the use of a wafer spinning module with an edge sensor which can belocated inside the track. Such a coarse pre-alignment technique is knownto those skilled in the relevant art(s) and so will not be discussedmore fully herein. While the observation of wafer location andorientation has been described in terms of a single camera, multiplecameras with narrow fields of view can be used to enhance the accuracyof the alignment. By using multiple cameras directed at differentviewpoints along the circumference of the wafer, the location of thecenter and the orientation of the notch can be more precisely determinedthan by using a single camera.

In a step 525, which can be performed concurrently with step 520, achuck is moved so as to align the wafer relative to the chuck. Asdescribed elsewhere herein, such a chuck can be an electrostatic chuck,a vacuum chuck, and the like. The chuck is moved relative to the waferthrough the use of an alignment stage like that described in connectionwith FIG. 2B. Movements of the alignment stage are controlled by thesame pattern recognition unit that receives data from the camera used toobserve the wafer. The pattern recognition unit knows the preciselocation of the wafer. The pattern recognition unit also knows theprecise location of the alignment stage by virtue of location feedbackfrom the alignment stage. By direct observation of the chuck with thecamera, the pattern recognition unit can cause the alignment stage tomove the chuck relative to the wafer until the wafer is aligned relativeto the chuck (the diameter of the chuck is purposely a little largerthan the diameter of the wafer).

Once the chuck and wafer are aligned relative to one another, asubsequent step 530 of placing the chuck in contact with the wafer isperformed. This can be accomplished, for example, by moving the chuckupwards until it is in physical contact with the wafer's bottom surface.As described above in connection with FIG. 2A, the chuck can have, forexample, cutouts to accommodate the wafer supports holding the wafer.Thus, when the chuck is moved upwards into contact with the wafer'sbottom surface, the wafer supports will not interfere with the chuckbecause they are located within the chuck cutouts. Once the chuck isplaced in contact with the wafer, the chuck is secured to the wafer in anext step 540. Securing the chuck to the wafer can be accomplished bycharging the chuck, in the case of an electrostatic chuck.Alternatively, securing the chuck to the wafer can be performed byactivating a vacuum within a vacuum chuck. Other methods of securing thechuck to the wafer can be performed without departing from the scope ofthe present invention.

Once the wafer has been secured to the chuck in step 540, the chuck canbe moved around within a lithography system according to the presentinvention all the while maintaining alignment with the wafer. Since thechuck is equipped with kinematic mounting features, the alignment of thewafer relative to the exposure stage will always be within therepeatability of the kinematic mounts used within the lithographysystem. Typically, the repeatability of such kinematic mounts is withinapproximately two microns. On the other hand, the repeatability of arobot and gripper is typically a few hundred microns. Therefore, theconventional steps of performing fine alignment subsequent to robotmovements can be avoided by moving wafers while attached to chucks. Finealignment will still be needed. Performing fine alignment subsequent torobot movements, however, facilitates the fine alignment process. Thus,a lithography system according to the present invention, as describedabove in connection with FIG. 1, can achieve high levels of throughput,for example 120 wafers per hour, by using multiple chucks within thesystem.

While the present invention has been described in terms of a lithographysystem working within a vacuum, the present invention could beimplemented as a non-vacuum system without departing from the scope ofthe present invention. In such a system, what has be described above asan alignment load-lock could be an alignment and chucking stationwithout the pump-down and venting characteristics of a load-lock.Moreover, a method could be performed according to the present inventionwithout the described pump-down and venting steps.

Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details can be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method, comprising: (a) aligning a substrate with respect to asubstrate support within a chamber; (b) adjusting a pressure within thechamber from a first pressure to a second pressure substantiallysimultaneously during step (a); (c) securely coupling the alignedsubstrate to the substrate support in the chamber; and (d) transportingthe securely coupled and aligned substrate on the substrate support fromthe chamber to another chamber.
 2. The method of claim 1, wherein thesecurely coupled and aligned substrate is transferred from the chamberto the another chamber having the second pressure via an area having thesecond pressure; and wherein the method further comprises: (e)patterning the securely coupled and aligned substrate in the anotherchamber.
 3. The method of claim 1, further comprising: using a load-lockas the chamber; and using a patterning chamber as the another chamber.4. The method of claim 1, wherein step (a) comprises: kinematicallyaligning the substrate support to an aligning stage; measuring aposition of the substrate with respect to the substrate support using acamera; generating position signals with the camera based on themeasuring step; and using the aligning stage to perform the aligningbased on the position signals.
 5. The method of claim 4, wherein thekinematically aligning comprises aligning a hemisphere on a surface ofthe substrate support with a vee-block on a surface of the aligningstage.
 6. The method of claim 4, further comprising: electricallycoupling the substrate support to the aligning stage.
 7. The method ofclaim 6, wherein the electrical coupling comprises receiving a pogocontact protruding from the aligning stage in a contact pad on thesubstrate support.
 8. The method of claim 1, further comprising using aload-lock as the chamber.
 9. The method of claim 1, further comprisingusing a electrostatic chuck as the substrate support.
 10. The method ofclaim 1, further comprising using a vacuum chuck as the substratesupport.
 11. The method of claim 1, wherein: step (a) further comprisesaligning multiple ones of the substrate with respective multiple ones ofthe substrate support; and step (c) further comprises securely couplingthe multiple ones of the aligned substrate to the respective multipleones of the substrate support.